The present invention relates generally to particle generators, and more particularly to a particle generator system incorporating a plurality of Laskin type nozzles.
Numerous nonintrusive fluid flow measurement techniques rely on particle seeding the flow field. Laser Fringe Anemometry and Laser Transit Anemometry rely on particles passing through light and dark regions produced at the focal point of the anemometer system. Particle Image Velocimetry is a method by which a double pulsed laser sheet illuminates particles in a flow region; knowing the time between the two laser pulses allows numerous particles to be tracked, which results in a vector plot of the entire flow region in the plane of illumination. Doppler Global Velocimetry is a method for measuring the flow field in a plane of illumination, and relies on the Doppler frequency shift in the scattered laser light resulting from the movement of numerous particles in the illuminated plane of the flow field. In all of these methods, precision depends directly on the ability of the particles to accurately represent the fluid flow behavior.
Particles for flow measurement may be generated by various methods, including atomization, fluidization, sublimation and chemical reaction (including combustion). For compressor flow measurements, atomization techniques are most advantageous. Atomization with evaporation is a technique in which solid particles are mixed with a liquid carrier, and the slurry is atomized to provide solid particles to the flow once the liquid carrier evaporates. If the original solid particles in liquid suspension are a single size and do not coagulate in the atomization process, monodispersed particles are introduced into the flow field. Although monodispersed particles are obtained with a reasonable data rate, the liquid carrier often does not completely evaporate before entering the measurement location, resulting in a buildup of solid seed material on the test model and instrumentation. Evaporation also leads to local temperature variation in the flow field. Therefore, atomization with evaporation is considered unfavorable for certain applications, such as compressor research. A second atomization process comprises evaporation followed by recondensation and produces monodispersed particles in the flow field, but requires a more complex generating system than direct atomization. Direct atomization employs the liquid droplet as it is generated and is less complex than the other two atomization methods.
The invention solves, or substantially reduces in critical importance, problems with existing atomization methods by providing a direct atomization particle generating system for applications requiring controlled liquid droplet generation. The invention incorporates air dilution with submerged nozzles (commonly called Laskin or Laskey nozzles) utilizing a shearing process to create liquid droplets for injection into fluid flow. The droplets (seed particles) are useful for laser flow measurements. The embodiment of the invention disclosed in greatest detail utilizes four sheafing jets in each of four nozzles. Separate controls for nozzle pressure and air dilution pressure allows generation of a large range of particle sizes and concentrations. The system provides high data rates of pure liquid droplets which require no phase change or chemical reaction for flow measurement. Although the invention is most directly applicable to pure liquid atomization, it may be useful in other atomization techniques which require evaporation.
It is therefore a principal object of the invention to provide a particle generator.
It is a further object of the invention to provide a particle generation system incorporating a plurality of Laskin type nozzles.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.